As is known, measuring machines are generally provided with a fixed base or machine bed and a mobile unit designed to move a measuring head according to co-ordinate axes with respect to the machine bed in a measurement space located above the machine bed. The mobile unit generally comprises a main carriage, which is mobile along an axis that is longitudinal with respect to the machine bed, and one or more carriages carried by the main carriage, which are mobile along respective co-ordinate axes.
The machine bed can be monolithic, for example made of granite or cast iron, or else can comprise a set of components rigidly fixed to one another to form a substantially rigid structure. The machine bed generally has two functions: supporting and constraining the workpiece being measured, and defining a guide for the mobile unit, and in particular for the main carriage of the machine, along one of the co-ordinate axes of the machine.
Measuring machines of the aforesaid type are generally provided with a system for compensation of geometrical errors, i.e., of the measurement errors depending upon the constructional defects of the machine (for example, rectilinearity errors of the axes, defects of orthogonality between the axes, etc.).
Current compensation techniques, of a strictly geometrical nature, do not generally take into account the measurement errors deriving from the elastic deformations of the machine bed under the weight of the workpiece to be measured. When the workpiece to be measured has a considerable weight (for example, in the case of dies, engine parts, castings of large dimensions) said errors may be non-negligible and jeopardize the accuracy of the machine.